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As climate change makes wet places wetter and dry areas drier, the frequency of drought is expected in increase in certain locations. Droughts, such as this one in Kenya in 2006, can increase food insecurity, especially among the poor.
(Brendan Cox/Oxfam/Flickr)

Eight Ways That Climate Change Hurts Humans

From floods and droughts to increases in violent conflict, climate change is taking a toll on the planet's population

Heat waves: Extreme heat can be deadly, particularly among the poor who may not have the luxury of retreating to air-conditioned rooms. In Australia, for example, the number of dangerously hot days is expected to rise from its current average of four to six days per year to 33 to 45 by 2070. That will translate to more deaths: About 500 people died because of heat in Australian cities in 2011; the Australian government has projected 2,000 deaths per year by the middle of this century.

Floods: Climate change tends to make wet areas wetter and dry areas drier, and so there will be an increase in both flooding and droughts. Flooding is one of the most common natural disasters. Floods displace people from their homes, damage and destroy infrastructure and buildings, and take a toll on an economic level. In 2011 alone, 112 million people worldwide were affected by floods, and 3140 people were killed.

Drought: Unlike a flood, drought is rarely a direct killer. But extremely dry conditions that last for months or years can lead to food and water shortages and rising food prices, which can contribute to conflict. Droughts also have huge economic costs, even in developed countries. New Zealand, for instance, lost more than $3 billion from 2007-2009 because of reduced farm output from drought.

Crop declines and food shortages: Extreme weather events, such as floods and droughts, will lead to declines in some crops in some areas. While this might be an inconvenience for people in developed countries when it comes to foods like limes and avocados, the situation will be far more dire when it comes to crops like corn and wheat and in countries that already struggle to feed their populations. Food shortages and increases in food prices, which increase the number of malnourished people, are a particular concern in those places that already suffering from food insecurity, such as large portions of Africa.

Infectious diseases: “Climate may act directly by influencing growth, survival, persistence, transmission or virulence of pathogens,” the IPCC scientists write in Chapter 11. Mosquitoes are sensitive to climate—as temperatures rise, they'll find favorable habitats in places that were once too cool for them to live, such as higher latitudes and altitudes. The diseases they transmit, such as malaria, dengue fever, and chikungunya fever, will spread with them.

Studies show that even a small amount of warming can increase malaria transmission under the right conditions. Dengue fever is another worry; it’s increased 30-fold in the last 50 years. And thanks to infected travelers' ability to move across the globe, chikungunya fever has already spread from Africa and Asia to the Caribbean, and may be poised to cross into the mainland Americas—a warming climate will exacerbate this new-found lack of isolation.

Food- and water-borne diseases, too, are a concern. For example, heavy rainfall, which will continue to increase as climate changes, can promote the transmission of water-borne diseases, such cholera and others caused by Vibrio bacteria, particularly in places where there aren’t good methods for disposing of human waste.

Mental illness: Climate change can increase stress, and that is a problem when it comes to mental health. “Harsher weather conditions such as floods, droughts, and heat waves tend to increase the stress on all those who are already mentally ill, and may create sufficient stress for some who are not yet ill to become so,” the IPCC researchers write in Chapter 11.

"When you have an environmental insult, the burden of mental health disease is far greater than the physical," Steven Shapiro, a Baltimore psychologist who directs the program on climate change, sustainability and psychology for the nonprofit Psychologists for Social Responsibility (PsySR), told LiveScience earlier this year. "Survivors can have all sorts of issues: post traumatic stress disorder, depression, anxiety, relationship issues, and academic issues among kids." Slow-developing events like droughts have even been linked to increases in suicide.

Violence and conflict: Human violence rarely has a single cause, but many of the effects of climate change have the potential to contribute to conflict—water and food shortages, soil degradation that makes land less suitable for agriculture, the movement of people as they migrate from lands made less habitable. “Climate change can indirectly increase risks of violent conflicts in the form of civil war and inter-group violence by amplifying well-documented drivers of these conflicts such as poverty and economic shocks,” researchers write in the report’s Summary for Policymakers [pdf].

These aren't doomsday scenarios; this isn't fearmongering—we're already seeing an uptick in every item on this list. So anyone hoping to avoid the effects of climate change may be out of luck.

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